Under some circumstances, the secure sealing of containers is necessary. It is of particular importance if such containers hold dangerous substances, such as for example fissile materials. In most cases, the container lid is connected to the container body by the use of at least one sealing bolt. Most often such a sealing bolt contains some kind of integrity element, breaking in case of violation and thereby revealing that the container may have been tampered with. Such a breakable integrity element can be concealed somewhere within the sealing bolt, which makes it more difficult to differentiate between standard sealing bolts and sealing bolts with additional security features. Thereby the number of sealing bolts with security features necessary to securely seal a container may be reduced.
An example of a sealing bolt in its most basic design is disclosed in GB-A-2067699. In one of the embodiments of the disclosure, the seal head is connected to its stud by a frangible integrity element that breaks at a given torque during the fastening process. However, the bolt head shows no evidence that the frangible element is broken and stays in its initial position on a plastic cup. If an attempt is made, to remove the sealing bolt, by turning its head, the plastic cup is visibly damaged, thus indicating tampering. The problem of such a bolt is that, once the frangible element is broken, it is difficult to remove the stud from the screw joint. However, once the sealing bolt is removed, it can be replaced with another bolt of the same type without revealing that the container has been tampered with.
To further increase the security of sealing bolts, an identification element may be concealed inside the sealing bolts so as to reveal if the initial sealing bolt has been replaced by another sealing bolt of the same type. If the identity of the sealing bolt is different and/or the integrity element is broken, the sealing device or/and the contents of the container may have been tampered with.
EP 0 658 250 B1 relates to a solution to univocally identify the sealing bolt by adding two ultrasonic elements to the breakable security element. Each ultrasonic element possesses one identification signal, wherein an overlap of the two identification signals provides a third identification signal. By comparison of the identification signals tampering can be revealed.
Even if the existing sealing bolts already seal the containers very securely, there still is a need not only to further improve the security, but also to reduce the maintenance effort necessary for the secure sealing of such containers.